Continuous variable transmission (CVT) is a user and environmentally friendly automatic type transmission that can be used in different industries as well as in transportation. In vehicles, the control unit as a separated unit connected here which is responsible to the gear ratio changing, causing transmission automatically selects the gear ratio that is the exact ratio needed to the road speed in which the car is driven in. Basically, the purpose of CVT is to continuously vary the transmission ratio. The idea of CVT is known for years; however, to date, its implementation especially in vehicles had faced different problems.
Three types of CVT were developed; the friction CVT, which vary the radius of the contact point between two rotating objects and this is the tangential velocity; the hydrostatic CVT that vary the fluid flow with variable displacement pumps into hydrostatic motors; and ratcheting CVT that vary the stroke of the reciprocating motion that is connected to a free wheel resulting in an unidirectional rotation. Each mechanical system has its own inherent limitations.
At the early decades of the 20century, one concept of the continuous transmission was developed by H. van Doorne. Experimental version was built in a Lloyd LP400 in the fifty's and eventually the first cars were ordered and produced by the DAF company. Although the technology of CVT actually dates back decades, these types of transmissions did not penetrate the car industry and has until recently been limited mostly to smaller cars with transversely-mounted engines and front wheel drive. Only in the recent years, there are attempts to drive the CVT into the mainstream of the automobile industry.
Other transmissions were developed and another example is the CLAAS'CVT. Primary components of the HM transmission of CLAAS are a reverse unit, hydrostatic unit, double planetary gear and low and high speed coupler shafts, and a multistep reduction gear downstream of the coupler shaft. The power is split in the reverse unit into mechanical and hydro static paths.
Audi's engineers developed a multitronic CVT for years and now stating that the multitronic finally overcomes all the drawbacks of the stepless principles. This CVT is an improvement of the van doorne CVT type based on chain V-belt principle. A key element of the multitronic is a variator that adopts a new transmission element called a link-plate chain made entirely from steel and is almost as flexible as V-belt so to handle high forces and torque levels of the A6's engine. However, after few years of employing the multitronic in Audi cars, reports from customers show that after a certain amount of mileage, the multitronic is experiencing failure.
It appears that other CVT transmissions are also experiencing failure after a certain mileage. It is therefore a long felt need to develop a CVT that inherently have the potential benefits of the CVT transmission and can work for a long time without or with minimal failure.
There is a need for an efficient transmission that will be able to replace the conventional manually or automatics gears that are operated using steps in the gear ratio.